Polymeric fibers and filaments are used to make a variety of products including yarns, carpets, woven fabrics, and nonwoven fabrics. As used herein, polymeric fibers and filaments are referred to generically as polymeric strands. Filaments mean continuous strands of material and fibers mean cut or discontinuous strands having a definite length.
Some products made with polymeric strands must be wettable with water or aqueous solutions. In other words, some products made with polymeric strands must be hydrophilic. Nonwoven fabrics are particularly suited for making hydrophilic products. Such products include towels, wipes, and absorbent personal care products including infant care items such as diapers, child care items such as training pants, feminine care items such as sanitary napkins, and adult care items such as incontinence products. Typical polymers used to make wettable nonwoven fabric include linear polycondensates such as polyamides, polyesters and polyurethanes and crystalline polyolefins such as polyethylene, polypropylene, and copolymers of ethylene and propylene. However, such polymers are naturally hydrophobic and must be treated to become hydrophilic.
Methods for treating hydrophobic polymeric strands and materials made therewith include solution coating of wetting agents, internal incorporation of wetting agents, and plasma treatment. These methods are effective but suffer some drawbacks. For example, wetting agents, whether in a surface coating or internally incorporated into the polymer, are fugitive and wash-off of the material after one or more wettings. Once the surface agent has been washed-off the polymer, the polymer becomes hydrophobic again and repels water. Plasma treatment is slow and costly and thus commercially impractical.
Naturally hydrophilic polymers for making polymeric strands are known. These polymers do not require any treatment to become wettable but suffer from some disadvantages. For example, U.S. Pat. Nos. 4,163,078; 4,257,999; and 4,810,449 each disclose hydrophilic filaments or fibers made by solution spinning acrylonitrile copolymers. Solution spinning is relatively costly and requires the use of organic solvents which are a potential environmental hazard. Melt-extruded, hydrophilic fibers for making fibers and filaments are known, but are uncommon and expensive and thus are not normally commercially feasible.
Therefore, there is a need for low-cost, permanently hydrophilic polymeric fibers and filaments and products such as nonwovens made therewith.